Image-pickup apparatus and a zoom lens for the image-pickup apparatus, with distortion correction

ABSTRACT

An image-pickup apparatus includes an image-pickup element that photoelectrically converts an optical image formed by an image-pickup optical system having a zoom function, and a correcting part that performs correction processing for a distortion component in image data generated based on an output from the image-pickup element, the distortion component corresponding to a distortion of the image-pickup optical system. The image-pickup optical system provides a first zoom range in which a distortion amount at a certain image height is larger than a predetermined value and a second zoom range in which a distortion amount at the certain image height is smaller than the predetermined value. The correcting part performs the correction processing so that the distortion component remains in a first corrected image data in the first zoom range is larger than the distortion component remaining in a second corrected image data in the second zoom range.

BACKGROUND OF THE INVENTION

The present invention relates to an image-pickup apparatus such as adigital still camera or a digital video camera having an electronicdistortion correction function and relates to an interchangeable lensmounted to the image-pickup apparatus.

The image-pickup apparatus capturing an image (image data) using asolid-state image-pickup element such as a CCD sensor or a CMOS sensorincludes an image-pickup optical system equipped thereto or detachablymounted thereto. Along with a trend for the miniaturization of theimage-pickup apparatus, the image-pickup optical system also is beingmade miniaturized. The miniaturization of the image-pickup opticalsystem, however, makes it more difficult to correct optical aberrationssufficiently. Thus, the captured image data often has to be subjected tothe processing of electronically correcting the aberration componentthereof.

Japanese Patent Laid-Open No. 2005-286482 discloses a method of, basedon an image-height vs. distortion data indicating a relationship betweena coordinate position of image data and a distortion at each imageheight, correcting a distortion component of the image data due to thedistortion in the image-pickup optical system.

Japanese Patent Laid-Open No. 2006-270918 discloses a method ofcorrecting a distortion component for image data using data indicating adistortion corresponding to a zoom position and an object distance of animage-pickup optical system.

The distortion correction methods disclosed in Japanese Patent Laid-OpenNo. 2005-286482 and Japanese Patent Laid-Open No. 2006-270918, however,try to achieve accurate distortion correction over the entire zoom rangeof the image-pickup optical system, which causes deterioration in imagequality instead.

Note here that a distortion amount at each image height of animage-pickup optical system, in general, changes with a zoom position ofthe image-pickup optical system. For instance, a zoom position closer tothe wide-angle end means an increase in the distortion amount.

On the other hand, the distortion correction processing of image data isbasically a coordinate transformation processing in which eachcoordinate (each pixel) of image data including a distortion componentis transformed into a coordinate from which the distortion component hasbeen removed or decreased, the distortion component being obtained bythe calculation based on data concerning the distortion. Such coordinatetransformation processing leads to a decrease in resolution of thecorrected image data, i.e., deterioration in image quality.

In addition, the accurate distortion correction performed over theentire zoom range of the image-pickup optical system results in a largeload on a calculating circuit that performs calculation for thecorrection or an increase in memory capacity that stores data relatingto the distortion used for the calculation.

Especially in the case of an image-pickup apparatus required to output areal-time image with continuity rather than a high-quality image, suchas in the case of a monitoring camera, excessive distortion correctionprocessing and a large calculation load may degrade the performance asthe image-pickup apparatus.

BRIEF SUMMARY OF THE INVENTION

The present invention provides an image-pickup apparatus enablingdistortion correction processing favorably performed within a range thatdoes not cause image deterioration in image data acquired using theimage-pickup apparatus whose distortion amount varies with its zoomstate, and provides an interchangeable lens used for the image-pickupapparatus.

The present invention further provides an image-pickup apparatusenabling image data of a favorable image quality at each zoom state,while suppressing an increase in calculation load and memory capacityfor distortion correction, and provides an interchangeable lens used forthe image-pickup apparatus.

An image-pickup apparatus as one aspect of the present inventionincludes an image-pickup element that photoelectrically converts anoptical image formed by an image-pickup optical system having a zoomfunction, and a correcting part that performs correction processing fora distortion component in image data generated based on an output fromthe image-pickup element, the distortion component corresponding to adistortion of the image-pickup optical system. The image-pickup opticalsystem provides a first zoom range in which a distortion amount at acertain image height is larger than a predetermined value and a secondzoom range in which a distortion amount at the certain image height issmaller than the predetermined value. The correcting part performs thecorrection processing so that the distortion component remains in afirst corrected image data obtained by correcting the image datagenerated in the first zoom range is larger than the distortioncomponent remaining in a second corrected image data obtained bycorrecting the image data generated in the second zoom range.

An image-pickup apparatus as another aspect of the present inventionincludes an image-pickup element that photoelectrically converts anoptical image formed by an image-pickup optical system having a zoomfunction, and a correcting part that performs correction processing fora distortion component in image data generated based on an output fromthe image-pickup element, the distortion component corresponding to adistortion of the image-pickup optical system. The image-pickup opticalsystem provides a first zoom range in which a distortion amount at acertain image height is larger than a predetermined value and a secondzoom range in which a distortion amount at the certain image height issmaller than the predetermined value. The correcting part performs thecorrection processing in the first zoom range and limits the correctionprocessing in the second zoom range.

A lens that is detachably attached to the above image-pickup apparatusas another aspect of the present invention includes an image-pickupoptical system having a zoom function and providing a first zoom rangein which a distortion amount at a certain image height is larger than apredetermined value, and a second zoom range in which a distortionamount at the certain image height is smaller than the predeterminedvalue, and a memory that stores data used for the correction processingby the image-pickup apparatus.

Other aspects of the present invention will become apparent from thefollowing description and the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the configuration of an image-pickupapparatus that is Embodiment 1 of the present invention.

FIG. 2 is a block diagram showing the configuration of a correctionprocessing circuit in Embodiment 1.

FIG. 3 is a cross-sectional view of a zoom lens (numerical valueexample 1) used for the image-pickup apparatus of Embodiment 1.

FIG. 4 is a graph showing an optical distortion of the zoom lens ofEmbodiment 1 (numerical value example 1).

FIG. 5 is a graph showing a distortion component in image data after thedistortion correction processing in Embodiment 1.

FIG. 6 is a flowchart showing operations of the correction processingcircuit of Embodiment 1.

FIG. 7 is a block diagram showing the configuration of aninterchangeable lens and an image-pickup apparatus that is Embodiment 2of the present invention.

FIG. 8 is a cross-sectional view of a zoom lens (numerical value example2) used for an image-pickup apparatus that is Embodiment 3 of thepresent invention.

FIG. 9 is a graph showing an optical distortion of the zoom lens ofEmbodiment 3 (numerical value example 2).

FIG. 10 is a graph showing an enlarged wide-angle end side portion ofFIG. 9.

FIG. 11 is a graph showing a distortion component in image data afterthe distortion correction processing in Embodiment 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will hereinafter bedescribed with reference to the accompanying drawings.

Prior to the description of specific embodiments, basic concepts of theembodiments of the present invention will be described below.

In the following description, a distortion and an amount thereofoccurring in an image-pickup optical system are referred to as anoptical distortion and an optical distortion amount, respectively. Adistortion and an amount thereof (magnitude) included in image data inaccordance with the optical distortion are referred to as a distortioncomponent and a distortion component amount, respectively. Thecorrection processing of an electronic distortion component for theimage data is referred to as distortion correction processing. The imagedata may be referred to as an image simply.

As described later, in Embodiments 1 and 2, in a first zoom range at awide-angle end of an image-pickup optical system having a zoom function(hereinafter called a zoom lens) or in the vicinity thereof where anoptical distortion at a certain image height is larger than apredetermined value (or the predetermined value or larger), thedistortion correction processing permitting the remainder of adistortion component to some extent is performed by a correcting part.In other words, the distortion correction processing in the first zoomrange is performed (a correction factor is selected) so that adistortion component remains in the image data more than in a secondzoom range after the distortion correction processing.

In further other words, the correcting part performs the correctionprocessing so that the distortion component remains in a first correctedimage data obtained by correcting the image data generated in the firstzoom range is larger than the distortion component remaining in a secondcorrected image data obtained by correcting the image data generated inthe second zoom range.

In the second region, an optical distortion at the certain image heightis smaller than the predetermined value.

This is because, since the resolution of the image decreases and imagequality deteriorates inversely with the correction amount of thedistortion component, the distortion component of 0 does not necessarilymean the ideal. For instance, when the distortion correction processingis performed so as to leave the distortion component of 0.5% or more, animage with a less distortion component can be obtained while avoidingthe deterioration in image quality due to excessive correction.

On the other hand, in the second zoom range, distortion correction witha maximum high accuracy can be performed, which means to minimize aremaining distortion component.

According to Embodiments 1 and 2, an image of a favorable image qualitywith a less distortion component can be obtained over the entire zoomrange while suppressing deterioration in image quality (decrease inresolution) resulting from the distortion correction processing in thefirst zoom range with a large optical distortion. In addition, since thedistortion correction processing with excessive high accuracy is notperformed in the first zoom range, the calculation load can be reduced,thus shortening the time required for the distortion correctionprocessing.

In Embodiment 3 described later, the switching is performed inaccordance with the zoom range as to whether or not to perform thedistortion correction processing. More specifically, in a first zoomrange where the optical distortion amount at a certain image height islarger than a predetermined value (or the predetermined value orlarger), the distortion correction processing is performed, whereas in asecond zoom range where the optical distortion amount at the certainimage height is smaller the predetermined value, the distortioncorrection processing is limited, i.e., not performed (prohibited). Thedistortion correction processing in the second zoom range may beperformed so that deterioration of image quality caused by thedistortion correction processing is smaller than that caused by thedistortion correction processing performed in the first zoom range.

In a zoom range where the optical distortion amount is originally small,a favorable image can be obtained without the distortion correctionprocessing. Thus, the distortion correction processing is performed onlyin the first zoom range where the distortion component in the image isconspicuous, whereby favorable image data can be obtained in each zoomrange while suppressing an increase in calculation load and memorycapacity.

For instance, in the case where the distortion correction processing isperformed in a zoom range (the second zoom range) with an absolute valueof the optical distortion of less than 1% at the image height with animage height ratio of 70% with reference to the maximum image height ofthe image-pickup element, a difference between non-corrected coordinates(x, y) and corrected coordinates (X, Y) often will not be 1 pixel ormore. Therefore, the distortion correction processing in this rangecauses a problem of the deterioration in resolving power being moresignificant than the effect of the distortion correction processing.Therefore, it is preferable that the distortion correction processing isnot performed in the zoom range with an absolute value of the opticaldistortion of less than 1%.

In the case where a zoom lens is such a type of generating a negativelarger (barrel-shaped) distortion in a zoom range closer to a wide-angleend, whereas generating a smaller distortion amount closer to atelephoto end, the first zoom range where the distortion correctionprocessing is to be performed may be decided as follows. That is, thefirst range may be set as the whole or a part of the range from thewide-angle end to the zoom position where the absolute value of theoptical distortion at the image height with the image height ratio of70% of the maximum image height decreases firstly to be 1% (a portionobtained by removing the zoom position with the absolute value of 1%).Thereby, the distortion correction processing can be performed to theappropriate and only range, thus reducing a calculation load and arequired memory capacity.

Alternatively, the distortion correction processing may be performed(only) in a zoom range (the first zoom range) where the absolute valueof the optical distortion at the image height with the image heightratio of 70% of the maximum image height of the image-pickup element islarger than 3% (or 3% or larger). Further, the distortion correctionprocessing may be performed (only) in a zoom range where the absolutevalue of the optical distortion is larger than 5% (or 5% or larger).

In these cases, the distortion correction processing preferably isperformed as in Embodiment 1 so as to permit the remainder of thedistortion component to some extent.

In each embodiment, the distortion correction processing may beperformed by polynomial approximation where data for performing thedistortion correction processing (e.g., data concerning the opticaldistortion, hereinafter simply called distortion data) is set as aparameter. Thereby, a memory capacity for storing the distortion datatherein can be saved, and the correction result also can be smooth,which means a natural image.

Furthermore, when the distortion correction processing is performed, adistortion correction parameter may be decided in ranges obtained bydividing a light-receiving area on the image-pickup element into tworanges vertically or horizontally with reference to the optical axisposition of the image-pickup optical system. The reason is as follows.In a rotationally-symmetric optical system with reference to the opticalaxis, the optical distortion is represented with one parameter. In thiscase, however, the optical distortion has to be decomposed into verticaland horizontal distortion components when the distortion correction isperformed. Then, in each divided range, an optical distortion amount ora distortion component amount calculated from a magnification varyinglens position (zoom position) and a focus lens position (focus position)making up the image-pickup optical system is stored in a memory.Thereby, the calculation for the distortion correction processing can bespeeded up.

The light-receiving area may be divided into two exact halves verticallyand horizontally, and a correction amount for the distortion componentmay be calculated in each of the thus divided four ranges. Thereby, acorrespondence between the distortion, the image height, thenon-corrected coordinates (x, y) and the corrected coordinates (X, Y)can be obtained, which makes it easy to correspond them to thecorrection amount of the distortion component.

In each embodiment, since the distortion amount varies significantlywith the zoom position, the distortion data is preferably stored in amemory while being associated with the zoom position. However, to storethe distortion data for all zoom positions will make the memory capacitylarge. Therefore, the distortion data in a zoom range to which thedistortion correction processing is to be performed only may be storedin the memory, or only data from which the distortion data over theentire zoom range can be calculated by interpolation calculation may bestored in the memory.

Moreover, the distortion correction processing is performed so that acorrected image corresponding to a shape of the optical distortionamount (distortion curve) according to the zoom positions that theimage-pickup optical system originally has can be obtained. Thereby, anatural corrected image can be obtained at each zoom position.

When the distortion correction processing is performed, correction forchromatic aberration of magnification (edge processing) may also beperformed. Thereby, a high-resolution image with a clear edge can beobtained. For instance, in the case of image data having red, green andblue signals, data for correcting the chromatic aberration ofmagnification may be determined in accordance with the amounts ofchromatic aberration of magnification of the red and blue signals withreference to the green signals.

Embodiment 1

FIG. 1 illustrates the configuration of an image-pickup apparatus thatis Embodiment 1 of the present invention. In the present embodiment andother embodiments described later, the image-pickup apparatus intendedis a video camera preferable to a monitoring camera. The configurationand the features of each embodiment, however, are not limited to themonitoring camera, and can be applied to general image-pickupapparatuses as well.

In FIG. 1, reference numeral 100 denotes a zoom lens as an image-pickupsystem having a zoom function, which forms an object image (opticalimage). The zoom lens 100 includes, in order of distance from theobject, a variator 101 that moves in the optical axis direction to varythe magnification, an aperture stop 103 that adjusts the light amount,and a compensator 102 that moves in the optical axis direction tocompensate the variation of image plane resulting from the focusing andthe magnification varying.

Reference numeral 104 denotes an image-pickup element, which may be aphotoelectric conversion element such as a CCD sensor or a CMOS sensor.An analogue output signal from the image-pickup element 104 is convertedinto digital image data by an A/D converter 105. The digital image data(hereinafter simply called image data) is then input to a correctionprocessing circuit 108 as the correcting part. The correction processingcircuit 108 causes an image memory 106 to store the image datatemporarily.

The zoom control, the aperture stop control and the focus control of thezoom lens 100 are performed by a camera microcomputer (hereinaftersimply called a microcomputer) 111 made up of a CPU or the like. Themicrocomputer 111 refers to the memory, as needed, for appropriateprocessing.

Reference numeral 110 denotes a selector, which reads out data(distortion data) relating to optical distortion of the zoom lens 100from a distortion memory 112 in accordance with a zoom position (zoomrange) and sends the same to the correction processing circuit 108.

The distortion memory 112 stores distortion data discretely at fourrepresentative image heights (30% image height, 50% image height, 70%image height, and 90% image height) at ten zoom positions representativeof the entire zoom range (hereinafter called representative zoompositions). Herein, N % image height means the image height where theimage height ratio becomes N % with respect to the image-pickup element104.

FIG. 2 illustrates the configuration of the correction processingcircuit 108 of FIG. 1. In FIG. 2, reference numeral 120 denotes adistortion correction amount calculating part. FIG. 6 is a flowchart ofthe processing performed by the distortion correction amount calculatingpart 120.

At Step S10 of FIG. 6, the distortion correction amount calculating part120 reads out, from the distortion memory 112, the distortion data atthe above-described representative image heights at the representativezoom positions.

Next, at Step S11, the distortion correction amount calculating part 120performs (polynomial) interpolation calculation using the distortiondata read out at Step S10 to calculate a continuous optical distortionamount at the representative image heights over the entire zoom range.

Next, at Step S12, the distortion correction amount calculating part 120acquires, from a zoom position detection part (111 a) in themicrocomputer 111, information indicating the current position of thevariator 101 (zoom position). Then, the distortion correction amountcalculating part 120 calculates optical distortion amounts atrepresentative image heights corresponding to the current zoom positionamong the optical distortion amounts over the entire zoom rangecalculated at Step S11.

Finally, at Step S13, the distortion correction amount calculating part120 performs (polynomial) interpolation calculation using the opticaldistortion amounts at the representative image heights corresponding tothe current zoom position calculated at Step S12 to calculate acontinuous optical distortion amount at all of the image heights from 0%image height to 100% image height corresponding to the current zoomposition.

Reference numeral 121 denotes a correction coordinate setting part,which sets corrected coordinates (X, Y) to be obtained by the conversionof non-corrected coordinates (x, y) based on the optical distortionamounts at all of the image heights corresponding to the current zoomposition calculated by the distortion correction amount calculating part120 (at Step S13).

Reference numeral 122 denotes a correction factor calculating part,which calculates a distortion correction factor used for the conversionof non-corrected coordinates (x, y) to corrected coordinates (X, Y) ofeach pixel in the image data.

Reference numeral 123 denotes a coordinate transforming part, whichmultiplies the coordinates of each pixel in non-corrected image datastored in the image memory 106 of FIG. 1 by the distortion correctionfactor calculated at the correction factor calculating part 122 tocalculate coordinates of each pixel of corrected image data. Thus,performing the coordinate conversion generates corrected image data.

The corrected image data is converted into an analogue image signal by aD/A converter 107 of FIG. 1, which is then output to the outside (e.g.,to the Internet, a network such as LAN, or an image recording apparatus)via an output terminal part 109.

The above-described polynomial interpolation calculation performed bythe distortion correction amount calculating part 120 (Steps S11 andS13) can decrease the amount of the distortion data to be stored in thedistortion memory 112. As a result, a distortion correction factor and apixel correction factor can be obtained using a less memory capacity,which are for obtaining corrected image data with natural appearance.

FIG. 3 and Table 1 show exemplary numerical values of the zoom lens ofthe present embodiment. These numerical values will be described later.

Referring now to FIGS. 4 and 5, the distortion correction processing forimage data in the present embodiment (exemplary numerical values) andthe effect thereof will be described below.

FIG. 4 illustrates an optical distortion (referred to as a distortion inthe drawing) of the zoom lens 100. It can be considered that adistortion component corresponding to this optical distortion isincluded in image data prior to the distortion correction processing. InFIG. 4, the horizontal axis represents a focal length, i.e., a zoomposition, and the vertical axis represents the amount and the directionof the optical distortion.

In FIG. 4, the absolute value of the distortion component at 90% imageheight (a certain image height) is larger than 1% (a predeterminedvalue) (1% or larger) over the entire zoom range. Therefore, thedistortion correction is performed thereto over the entire zoom range inthe present embodiment.

FIG. 5 illustrates a distortion component (referred to as a distortionin the drawing) included in the image data subjected to the distortioncorrection processing. In FIG. 5, the horizontal axis represents a focallength (a zoom position), and the vertical axis represents the amountand the direction of the distortion component.

As can be seen from this drawing, the remainder of the distortioncomponent at 70% image height is less than 1% over the entire zoomrange, which means the distortion correction processing performedfavorably.

Herein, as for the distortion component at 90% image height, theremainder between the focal length of 3.5 mm (wide-angle end) and 4.8 mm(a first zoom range) is larger than the remainder between the focallength of 4.9 and 9 mm (a second zoom range). The remainder in the firstzoom range is 0.5% or more.

In this way, the distortion correction processing is performed so as topermit the remainder of the distortion component to some extent, wherebythe above-stated effect can be obtained.

Embodiment 2

FIG. 7 illustrates the configuration of an interchangeable lens and animage-pickup apparatus to which the interchangeable lens is mounteddetachably that are Embodiment 2 of the present invention. Theseinterchangeable lens and image-pickup apparatus make up an image-pickupsystem.

In FIG. 7, reference numeral 400 denotes an image-pickup apparatus,including the elements 104 to 111 described in Embodiment 1 except forthe zoom lens 100 and the distortion memory 112. Since the functions ofthese elements 104 to 111 are the same as those in Embodiment 1, theexplanations thereof will be omitted.

Reference numeral 300 denotes the interchangeable lens. Referencenumeral 301 denotes a variator, 302 denotes a compensator, and 303denotes an aperture stop. These elements make up a zoom lens 310 as theimage-pickup optical system having a zoom function.

Similarly to the distortion memory 112 of Embodiment 1, theinterchangeable lens 300 is provided with a distortion memory 311 withdistortion data stored therein.

The camera microcomputer 111 in the image-pickup apparatus 400 requestsa lens microcomputer 312 provided in the interchangeable lens 300 totransmit distortion data stored in the distortion memory 311 andinformation on the current zoom position. In response to the request,the lens microcomputer 312 transmits the distortion data stored in thedistortion memory 311 and information on the current zoom positiondetected by a zoom position detector 312 a to the correction processingcircuit 108 of the image-pickup apparatus 400. The distortion correctionprocessing by the correction processing circuit 108 and the result arethe same as those described in Embodiment 1 referring to FIGS. 2 and 4to 6.

Embodiment 3

Referring to FIGS. 9 to 11, distortion correction processing for imagedata by an image-pickup apparatus that is Embodiment 3 of the presentinvention and the effects thereof will be described below. The presentembodiment can be applied to both of the lens-integral type image-pickupapparatus as in Embodiment 1 and the lens interchangeable-typeimage-pickup apparatus as in Embodiment 2. In either case, theconfiguration of the image-pickup apparatus and the interchangeable lensare the same as those described in Embodiments 1 and 2.

FIG. 8 and Table 2 illustrate exemplary numerical values of the zoomlens of the present embodiment. These numerical values will be describedlater.

FIG. 9 illustrates an optical distortion (referred to as a distortion inthe drawing) of the zoom lens of the present embodiment. It can beconsidered that a distortion component corresponding to this opticaldistortion is included in image data prior to the distortion correctionprocessing. FIG. 10 is an enlarged view of FIG. 9 illustrating theoptical distortion in the zoom range from the wide-angle end to thefocal length of 40 mm. In FIGS. 9 and 10, the horizontal axis representsa focal length, i.e., a zoom position, and the vertical axis representsthe amount and the direction of the optical distortion.

In FIGS. 9 and 10, the optical distortion amount at 90% image height (acertain image height) is smaller than 1% (a predetermined value) in thezoom range of the focal length between 13 and 120 mm (a second zoomrange). Therefore, the distortion correction processing (i.e., thecalculation for distortion correction) is not performed thereto in therange.

On the other hand, in the zoom range of the focal length between 3 mm(wide-angle end) and 12 mm (a first zoom range), the optical distortionamount at 90% image height is larger than 1% (1% or larger), andtherefore the distortion correction processing is performed in therange.

As shown in the enlarged view of FIG. 10, the zoom range to which thedistortion correction processing is to be performed is a limited rangefrom the wide-angle end to the focal length of 12 mm. Therefore, in thepresent embodiment, the execution and non-execution (limitation) of thedistortion correction processing is switched based on the current zoomposition detected by the zoom position detector (corresponding to 111 aof FIG. 1 or 312 a of FIG. 7).

As for the processing by the correction processing circuit(corresponding to 108 of FIGS. 1 and 7), a step of determining thecurrent zoom position may be provided prior to Step S10 of the flowchartof FIG. 6. Instead of Step S11 of FIG. 6, a step of calculating opticaldistortion amounts at representative image heights in the zoom range ofthe focal length between 3 mm and 12 mm may be provided.

The switching of the execution and the non-execution of the distortioncorrection processing performed between the focal length of 12 and 13 mmmay cause an output image in this zoom range to be unnatural. Thus, thedistortion correction factor may be decreased gradually to zero towardthe zoom position of the focal length from around 12 mm to 30 mm.

FIG. 11 illustrates a distortion component (referred to as a distortionin the drawing) included in image data subjected to the distortioncorrection processing. In FIG. 11, the horizontal axis represents afocal length (a zoom position), and the vertical axis represents theamount and the direction of the optical distortion.

As can be seen from this drawing, the remainder of the distortioncomponent is less than 1% over the entire zoom range and at all imageheights, which means the distortion correction processing performedfavorably.

In the present embodiment, the remainder of the distortion component inthe zoom range subjected to the distortion correction processing islarger than the remainder of the distortion component in the zoom rangethat is not subjected to the distortion correction processing (exceptfor the zoom range where the direction of the distortion component thatis originally close to 0% reverses). Especially, the remainders of thedistortion components at 90% image height and 70% image height in thefirst zoom range in the vicinity of the wide-angle end are 0.5% or more.

In this way, the distortion correction processing is performed so as topermit the remainder of the distortion component to some extent, wherebythe above-stated effect can be obtained.

In the above Embodiments 1 to 3, the distortion curve indicating theremainder of the distortion component corresponding to the zoompositions after the distortion correction processing has a shape similarto the distortion curve indicating the optical distortion amountcorresponding to the zoom positions prior to the distortion correctionprocessing. In this way, the distortion correction processing isperformed so as to hardly change the shape of the distortion curve, thusavoiding the image after the correction to be unnatural.

Numerical Value Example 1

FIG. 3 illustrates the optical configuration at a wide-angle end of azoom lens as a numerical value example of Embodiment 1. Table 1 showsspecific numerical values of the zoom lens of FIG. 3.

In FIG. 3, B1 to B3 denote lens units, among which B1 corresponds to thevariator 101 and B2 corresponds to the compensator 102 of FIG. 1. Themovement of each of the lens units B1 and B2 from the wide-angle end tothe telephoto end is indicated by an arrow below thereof.

B3 is a fixed lens unit, and G denotes a glass block such as an opticalfilter. IP denotes an image plane, at which an image-pickup element 104is disposed. SP denotes an aperture stop 103.

In Table 1, f denotes a focal length (mm), Fno denotes a F number, and ωdenotes a half viewing field. Ri denotes a curvature radius of an i-thlens face from the object side, and Di denotes a distance between thei-th face and an (i+1)-th lens face. Ni and vi denote a refractive indexof a material of an i-th lens element and an Abbe constant thereof,respectively. “e−m” means “×10 ^(−m)”.

Among the lens faces, the lens face with the mark “*” assigned theretoin Table 1 has an aspheric surface. The aspheric surface can berepresented by the following expression, where the X axis is in theoptical axis direction, the h axis is in the direction perpendicular tothe optical axis, and the light traveling direction from the object ispositive:

$\begin{matrix}{X = {\frac{\left( {1/R} \right)\mspace{14mu} h^{2}}{1 + \sqrt{\left\{ {1 - {\left( {1 + k} \right)\mspace{14mu}\left( {h/R} \right)^{2}}} \right\}}} + {Bh}^{4} + {Ch}^{6} + {Dh}^{8} + {Eh}^{10} + {B^{\prime}h^{5}} + {C^{\prime}h^{7}} + {D^{\prime}h^{9}}}} & \left\lbrack {{Expression}\mspace{20mu} 1} \right\rbrack\end{matrix}$

where, R denotes a paraxial curvature radius, k denotes a conicconstant, and B, C, D, E, B′, C′, and D′ denote aspheric coefficients.

These representations of the optical configuration are the same as inthe other numerical value examples.

TABLE 1 f = 3.52~6.47~8.88 Fno = 2.1~2.7~3.5 2ω = 65.2~38.4~28.4 R1 =500 D1 = 1 N1 = 1.48749 ν1 = 70.2 R2 = 7.20738 D2 = 2.74315 R3 =−179.539 D3 = 1 N3 = 1.48749 ν3 = 70.2 R4 = 10.49384 D4 = 2.37 R5 =9.29148 D5 = 1.6 N5 = 1.761821 ν5 = 26.5 R6 = 12.36689 D6 = VARIABLE R7= APERTURE STOP D7 = VARIABLE *R8 = 6.2371 D8 = 2.5 N8 = 1.6935 ν8 =53.2 R9 = ∞ D9 = 0.8 N9 = 1.698947 ν9 = 30.1 R10 = 6.16765 D10 = 0.471R11 = 14.8436 D11 = 2.4 N11 = 1.603112 ν11 = 60.6 R12 = −10.2412 D12 =VARIABLE R13 = 52.4 D13 = 2 N13 = 1.696797 ν13 = 55.5 R14 = −8.6 D14 =0.8 N14 = 1.805181 ν14 = 25.4 R15 = −32.9 D15 = 1.4 R16 = ∞ D16 = 2 N16= 1.51633 ν16 = 64.1 R17 = ∞ FOCAL LENGTH VARIABLE DISTANCE 3.52 6.478.88 D6 11.50 3.23 2.33 D7 7.75 4.15 1.20 D12 2.40 6.00 8.95 ASPHERICCOEFFICIENT *R8 k = −6.27256e−01 B = −1.46455e−04 C = 3.29397e−06 D =−6.85706e−08

Numerical Value Example 2

FIG. 8 illustrates the optical configuration at a wide-angle end of azoom lens as a numerical value example of Embodiment 3. Table 2 showsspecific numerical values of the zoom lens of FIG. 8.

In FIG. 8, B1 to B4 denote lens units, among which B2 corresponds to thevariator 101 and B4 corresponds to the compensator 102 of FIG. 1. Themovement of each of the lens units B2 and B4 from the wide-angle end tothe telephoto end is indicated by an arrow below thereof.

B1 and B3 are fixed lens units, and G denotes a glass block such as anoptical filter. IP denotes an image plane, at which an image-pickupelement 104 is disposed. SP denotes an aperture stop 103.

TABLE 2 f = 4.05~33.88~121.47 Fno = 1.85~2.41~4.09 2ω = 58.1~7.6~2.1 R1= 93.29921 D1 = 1.57895 N1 = 1.84666 ν1 = 23.9 R2 = 32.03515 D2 =7.75476 N2 = 1.69680 ν2 = 55.5 R3 = −432.06900 D3 = 0.33553 R4 =31.55042 D4 = 4.13060 N4 = 1.83481 ν4 = 42.7 R5 = 79.20390 D5 = VARIABLER6 = 42.30873 D6 = 0.98684 N6 = 1.88300 ν6 = 40.8 R7 = 7.94740 D7 =2.63145 R8 = −32.94490 D8 = 0.98684 N8 = 1.80400 ν8 = 46.6 R9 = 9.42246D9 = 1.79096 R10 = 12.65834 D10 = 2.35823 N10 = 1.92286 ν10 = 18.9 R11 =35.86117 D11 = VARIABLE R12 = APERTURE STOP D12 = 2.05931 *R13 =15.86489 D13 = 4.33576 N13 = 1.58313 ν13 = 59.4 *R14 = −44.52370 D14 =0.70142 R15 = 18.04706 D15 = 1.08553 N15 = 1.84666 ν15 = 23.9 R16 =12.22853 D16 = VARIABLE R17 = 26.23259 D17 = 5.35382 N17 = 1.65844 ν17 =50.9 R18 = −8.31712 D18 = 0.98684 N18 = 1.84666 ν18 = 23.9 R19 =−16.93690 D19 = 7.88022 R20 = ∞ D20 = VARIABLE N20 = 1.51400 ν20 = 60.0R21 = ∞ FOCAL LENGTH VARIABLE DISTANCE 4.05 33.88 121.47 D5 1.18 25.8031.96 D11 32.91 8.29 2.14 D16 11.39 4.95 15.64 D20 7.88 14.32 3.63ASPHERIC COEFFICIENT *R13 k = 4.647200e−01 B′ = −1.02406e−08 C′ =1.11769e−08 D′ = −3.81049e−10 *R14 k = −5.79269e+01 B′ = −6.52820e−06

According to the above-stated embodiments, distortion correctionprocessing is performed so as to permit the remainder of the distortionto some extent in a zoom range with a large distortion amount of theimage-pickup optical system, and therefore an image subjected to thefavorable distortion correction can be obtained while suppressingdeterioration in image quality.

According to the above-stated embodiments, distortion correctionprocessing is performed in a zoom range with a large distortion amountof the image-pickup optical system, while the processing is limited in azoom range with a small distortion amount. Therefore, a favorable imagedata can be obtained in each zoom range, while suppressing an increasein calculation load and memory capacity.

Furthermore, the present invention is not limited to these embodimentsand various variations and modifications may be made without departingfrom the scope of the present invention.

This application claims the benefit of Japanese Patent Application No.2007-179211, filed on Jul. 9, 2007, which is hereby incorporated byreference herein in its entirety.

1. An image-pickup apparatus comprising: an image-pickup element thatphotoelectrically converts an optical image formed by an image-pickupoptical system having a zoom function; and a correcting part thatperforms a correction processing for a distortion component in imagedata generated based on an output from the image-pickup element, thedistortion component corresponding to a distortion of the image-pickupoptical system, wherein the image-pickup optical system provides a firstzoom range in which an absolute value of a distortion amount at acertain image height is larger than a predetermined value and a secondzoom range in which an absolute value of a distortion amount at thecertain image height is smaller than the predetermined value, whereinthe correcting part performs the correction processing so that anabsolute value of the distortion component remaining in first correctedimage data obtained by correcting the image data generated in the firstzoom range is larger than an absolute value of the distortion componentremaining in second corrected image data obtained by correcting theimage data enerated in the second zoom range, and wherein in the firstzoom range, an absolute value of the distortion amount at an imageheight with an image height ratio of 70% with reference to a maximumimage height of the image-pickup element is larger than 1%.
 2. A lensthat is detachably attached to the image-pickup apparatus according toclaim 1, the lens comprising: an image-pickup optical system having azoom function and providing a first zoom range in which an absolutevalue of a distortion amount at a certain image height is larger than apredetermined value, and a second zoom range in which an absolute valueof a distortion amount at the certain image height is smaller than thepredetermined value; and a memory that stores data used for thecorrection processing by the image-pickup apparatus.
 3. An image-pickupapparatus comprising: an image-pickup element that photoelectricallyconverts an optical image formed by an image-pickup optical systemhaving a zoom function; and a correcting part that performs a correctionprocessing for a distortion component in image data generated based onan output from the image-pickup element, the distortion componentcorresponding to a distortion of the image-pickup optical system,wherein the image-pickup optical system provides a first zoom range inwhich an absolute value of distortion amount at a certain image heightis larger than a predetermined value and a second zoom range in which anabsolute value of a distortion amount at the certain image height issmaller than the predetermined value, wherein the correcting partperforms the correction processing so that an absolute value of thedistortion component remaining in first corrected image data obtained bycorrecting the image data generated in the first zoom range is largerthan an absolute value of the distortion component remaining in secondcorrected image data obtained by correcting the image data generated inthe second zoom range, and wherein the first zoom range is included in azoom range from a wide-angle end to a position where an absolute valueof the distortion amount at an image height with an image height ratioof 70% with reference to a maximum image height of the image-pickupelement decreases to be 1% firstly.
 4. A lens that is detachablyattached to the image-pickup apparatus according to claim 3, the lenscomprising: an image-pickup optical system having a zoom function andproviding a first zoom range in which an absolute value of a distortionamount at a certain image height is larger than a predetermined value,and a second zoom range in which an absolute value of a distortionamount at the certain image height is smaller than the predeterminedvalue; and a memory that stores data used for the correction processingby the image-pickup apparatus.
 5. An image-pickup apparatus comprising:an image-pickup element that photoelectrically converts an optical imageformed by an image-pickup optical system having a zoom function; and acorrecting part that performs a correction processing for a distortioncomponent in image data generated based on an output from theimage-pickup element, the distortion component corresponding to adistortion of the image-pickup optical system, wherein the image-pickupoptical system provides a first zoom range in which an absolute value ofdistortion amount at a certain image height is larger than apredetermined value and a second zoom range in which an absolute valueof a distortion amount at the certain image height is smaller than thepredetermined value, wherein the correcting part performs the correctionprocessing so that an absolute value of the distortion componentremaining in first corrected image data obtained by correcting the imagedata generated in the first zoom range is larger than an absolute valueof the distortion component remaining in second corrected image dataobtained by correcting the image data generated in the second zoomrange, and wherein the absolute value of the distortion componentremaining in the image data after the correction processing in the firstzoom range is larger than 0.5% at an image height with an image heightratio of 70% with reference to a maximum image height of theimage-pickup element.
 6. A lens that is detachably attached to theimage-pickup apparatus according to claim 5, the lens comprising: animage-pickup optical system having a zoom function and providing a firstzoom range in which an absolute value of a distortion amount at acertain image height is larger than a predetermined value, and a secondzoom range in which an absolute value of a distortion amount at thecertain image height is smaller than the predetermined value; and amemory that stores data used for the correction processing by theimage-pickup apparatus.
 7. An image-pickup apparatus comprising: animage-pickup element that photoelectrically converts an optical imageformed by an image-pickup optical system having a zoom function; and acorrecting part that performs a correction processing for a distortioncomponent in image data generated based on an output from theimage-pickup element, the distortion component corresponding to adistortion of the image-pickup optical system, wherein the image-pickupoptical system provides a first zoom range in which an absolute value ofdistortion amount at a certain image height is larger than apredetermined value and a second zoom range in which an absolute valueof a distortion amount at the certain image height is smaller than thepredetermined value, wherein the correcting part performs the correctionprocessing in the first zoom range and limits the correction processingin the second zoom range, wherein the correcting part performs thecorrection processing in the first zoom range so that an absolute valueof the distortion component remaining in first corrected image dataobtained by correcting the image data generated in the first zoom rangeis larger than an absolute value of the distortion component of theimage data generated in the second zoom range remaining in the imagedata, and wherein in the first zoom range, an absolute value of thedistortion amount at an image height with an image height ratio of 70%with reference to a maximum image height of the image-pickup element islarger than 1%.
 8. A lens that is detachably attached to theimage-pickup apparatus according to claim 7, the lens comprising: animage-pickup optical system having a zoom function and providing a firstzoom range in which an absolute value of a distortion amount at acertain image height is larger than a predetermined value, and a secondzoom range in which an absolute value of a distortion amount at thecertain image height is smaller than the predetermined value; and amemory that stores data used for the correction processing by theimage-pickup apparatus.
 9. An image-pickup apparatus comprising: animage-pickup element that photoelectrically converts an optical imageformed by an image-pickup optical system having a zoom function; and acorrecting part that performs a correction processing for a distortioncomponent in image data generated based on an output from theimage-pickup element, the distortion component corresponding to adistortion of the image-pickup optical system, wherein the image-pickupoptical system provides a first zoom range in which an absolute value ofa distortion amount at a certain image height is larger than apredetermined value and a second zoom range in which an absolute valueof a distortion amount at the certain image height is smaller than thepredetermined value, wherein the correcting part performs the correctionprocessing in the first zoom range and limits the correction processingin the second zoom range, wherein the correcting part performs thecorrection processing in the first zoom range so that an absolute valueof the distortion component remaining in first corrected image dataobtained by correcting the image data generated in the first zoom rangeis larger than an absolute value of the distortion component of theimage data generated in the second zoom range remaining in the imagedata, and wherein the first zoom range is included in a zoom range froma wide-angle end to a position where an absolute value of the distortionamount at an image height with an image height ratio of 70% withreference to a maximum image height of the image-pickup elementdecreases to be 1% firstly.
 10. A lens that is detachably attached tothe image-pickup apparatus according to claim 8, the lens comprising: animage-pickup optical system having a zoom function and providing a firstzoom range in which an absolute value of a distortion amount at acertain image height is larger than a predetermined value, and a secondzoom range in which an absolute value of a distortion amount at thecertain image height is smaller than the predetermined value; and amemory that stores data used for the correction processing by theimage-pickup apparatus.
 11. An image-pickup apparatus comprising: animage-pickup element that photoelectrically converts an optical imageformed by an image-pickup optical system having a zoom function; and acorrecting part that performs a correction processing for a distortioncomponent in image data generated based on an output from theimage-pickup element, the distortion component corresponding to adistortion of the image-pickup optical system, wherein the image-pickupoptical system provides a first zoom range in which an absolute value ofa distortion amount at a certain image height is larger than apredetermined value and a second zoom range in which an absolute valueof a distortion amount at the certain image height is smaller than thepredetermined value, wherein the correcting part performs the correctionprocessing in the first zoom range and limits the correction processingin the second zoom range, wherein the correcting part performs thecorrection processing in the first zoom range so that an absolute valueof the distortion component remaining in first corrected image dataobtained by correcting the image data generated in the first zoom rangeis larger than an absolute value of the distortion component of theimage data generated in the second zoom range remaining in the imagedata, and wherein the absolute value of the distortion componentremaining in the image data after the correction processing in the firstzoom range is larger than 0.5% at an image height with an image heightratio of 70% with reference to a maximum image height of theimage-pickup element.
 12. A lens that is detachably attached to theimage-pickup apparatus according to claim 11, the lens comprising: animage-pickup optical system having a zoom function and providing a firstzoom range in which an absolute value of a distortion amount at acertain image height is larger than a predetermined value, and a secondzoom range in which an absolute value of a distortion amount at thecertain image height is smaller than the predetermined value; and amemory that stores data used for the correction processing by theimage-pickup apparatus.